Yes switching to milk first then solids an hour later would be my first step.
At 6 months I really wouldn't want her milk to drop any further than it is already. 20oz is acceptable and in addition any dairy solids count towards that milk intake but it might be wise to remember that her formula is a complete meal with all the balance of vitamins and minerals whilst solids or dairy solids are not.
Switching to milk first may not show any effect in just one or two days, you may need to stick at it longer to help change the balance of milk/solids, the same goes for reducing or cutting one of the solids meals, it would take several days for her to get the idea that she needs to take more milk.
LOs are generally good at self regulation and meeting their needs but I would be cautious of allowing her day time bottles to drop at this age, it is not advised. If it was me I'd take her to a very quiet, possibly dimly lit room with no distractions for her bottle feeds and reduce solids until she gets the message to take her milk.
I know people will suggest me to give milk first then solids after the first nap but trust me she just won't take it
This is where you need to decide whether to trust her choice or to put your foot down as her parent. Whilst you say 'trust me she will not take it', she is not the one in charge, she's 6 months old and it is ultimately for you to decide what is best.
I would switch to milk first solids second but I would also bring the solids a bit closer to the milk time so that there is a longer time gap between the solids and her next milk feed, giving her time to build up more of an appetite. Something like:
7.00 milk
8.00 breakfast
9.30 nap
11.30 milk
12.00/12.30 lunch
2.00 nap
4.30 milk (or earlier if the nap ends earlier)
5.30 solids (or cut this meal altogether)
7.00 milk
11 DF milk
4 NF milk
it might also be that she is dropping milk in the day and preferring solids due to there being two night feeds. Rather than allowing her to drop her day time milk I would be more inclined to gradually wean the night feed so she has more appetite for milk in the day, leaving 4 decent day time milk feeds and the DF.
hope this helps