Hi, welcome to BW forums
The chances are your LO is just going through a brief phase of eating less solids, most likely due to teething or recovery from the illness you mentioned. Often with LOs this young there can be quite a difference between what they eat during a growth spurt, what they eat on a 'normal' day, and what they eat when they are teething or feeling poorly. As parents we can get used to the increased appetite of a certain phase and then become worried when appetite drops down again. It sounds totally normal so try not to worry.
I don't think you need to reduce her milk intake to encourage more solids to be taken but there are one or two things you might consider changing slightly in the routine which might help to find the time when she is more interested in solids and less likely to spit food or drop it to the floor.
Babies tend to have a bigger appetite in the morning and early afternoon hours, not so much in the evening. How about you introduce a breakfast solids meal around 8am? You could then give a milk feed at 11am after her nap, move lunch a little later. I would not expect her to take much solids at the evening meal because of LO's tendency to take more in the earlier hours and also often they seem to need the evening meal to come quite early. It's not unusual to see the evening meal closer to 4.30pm but if you want to sit together as a family at 6pm this is fine (I am a big fan of family meals) just don't expect her to take very much but rather she joins you for the family aspect of coming together.
The times I'm suggesting would look something like this:
7am milk
8am breakfast solids
11am milk
12pm lunch solids
3pm solids snack with milk drink
4.30pm solids dinner
6pm family dinner (she may not eat much but can enjoy the social aspect and be offered family food)
8.30pm milk (if BT moves earlier this milk is fine to be earlier, BT looks quite late but if your sleep routine is working then that's fine)
This is not a hard and fast rule on feed times but you might find she is more interested in solids at these times. In a month or two you could then switch the 11am milk to a snack, keeping at least 2 good milk drinks, one at WU and one at BT.
You are absolutely right that her spitting and dropping food is an indication that she does not want to eat the food. She seems happy to taste the foods to explore how they smell, feel, taste, and the texture in her mouth which is great, she is just not hungry at those times to eat them. It may be she is not hungry at all or may be she is off food due to teething or illness.
It's ok to stop her dropping the food by gently holding her hand as she is about to drop it and guiding her hand back over the tray/table to drop the food, or gently remove it from her hand. I used to quickly put a bowl under my DS's hand so the food dropped into there and at the same time said "Let's clean up" and show him how to clear all his pieces of food into the bowl I provided, carefully and gently preventing him from dropping food to the floor and positively thanking him for any pieces he managed to get into the bowl. When he was cooperative I let him clear up more pieces, when he was more determined to drop food to the floor I made sure I was fast at collecting the bits up to keep the whole process as positive as possible.
If the dropping becomes a big issue I would reduce how much food you give her in one go. A bowl of food out of her reach can hold the full portion, you then give her one piece to eat at a time. This sets her up for success instead of providing her with lots of food ammunition.
It is also ok to say "food is for eating, when you are finished eating tidying up please" "If you are not hungry tidy up please, here drop into this bowl..." (focus on the action you want rather than the action you do not want). I would also ignore any food which makes to the floor, not tidy it whilst she is still in her chair as this can rapidly become a game of baby drop food, mummy pick up food, it is almost like a game of throw catch, her actions cause your actions, the way to avoid this is to leave those pieces until the end of the meal and she is out of her chair. Then clear up the few pieces which made it to the floor, this distances your actions from hers and no game is made of it.
I would not pat her hand or demonstrate any kind of physical punishment for dropping food - all this will teach her is that it's OK to hit people. You are the person she is learning from, if you show her it is OK to hit (even a pat) she will copy this. If you show her food is enjoyable to eat, how to use cutlery, how to clean up, how to resolve problems without hitting, she will want to copy this.
You might want to offer her some cause and effect toys to play with, things (not food) which are ok to drop and watch what happens. LOs love to play "fill and dump" with all sorts of containers and items for dumping. This helps develop their understanding of the world around them and offering plenty of chances for this during activity time may help prevent this game being played with food at meal times.
I hope this helps.