Hugs to you both with all the nw's.
Yay for the better napping! I found with my DD that she napped well until around 8-10 weeks and then would do these annoying 45 min naps that you could set a clock to! I tried to extend her naps with a modified shh-pat (it was really shh-rub on the tummy since she was on her back) and it took until she was around 4.5 months and then she figured out how to transition without me helping her. So, it sounds like your DD is learning how to transition between sleep cycles during the day. with better napping, it will be easier to have a 4 hr easy.
WRT feeding and snacking.. around this age I found a couple of things... they get distracted while eating, especially during the day (hence easier to take full feeds at night), snacking can become habit... so, if you are not already doing this, try to feed her during the day in a quiet room, dim lights, calm environment, etc. Hopefully she will take a better feed. At her last well baby visit, how is her weight gain? Both of my babies were small at birth and lost weight and were some what slow to re-gain so I got many a lecture about feeds, etc. If she's on a growth curve and not falling off a curve, meeting developmental milestones, etc I would encourage you to aim for a 3.5 to 4 hr easy for feeds as they will feed more efficiently. With snacking they will feed more often but often just get lots of fore milk and not enough of the hind milk which has a lot of the fat.
WRT feeding at night. it's not uncommon for babies to take two feeds during the night. I would aim to feed her if she's gone at least 3 hrs between feeds. I know its hard because you are so exhausted... it's easier to feed her than to try to re-settle. If you can have your DH help out on the weekend, that is great. He can settle her if she wakes more frequently.
When she wakes at night, what is she doing? crying?
Reasons for NWs... hunger is obviously one reason for nws but there are others.... teething. With my two kids, I've noticed that for some babies, the movement of the teeth is more painful (e.g. my DS) whereas for others, its the cutting (e.g. my DD). So, you might not see the bumps or that she's starting to cut her teeth but she could still be waking due to teething pain. The other is the 4 month sleep regression due to developmental milestones. This can take weeks to sort out unfortunately but the key here is to follow your usual routine and try to re-settle without introducing any new props. how she is waking in the night may tell us what the issue is.
HTH