Hello and welcome to BW forums
The guidance A time for 6 months is 3hrs awake so if your LO is sleeping after only 2hrs the chances are she is UT (undertired) and unable to transition to the next sleep cycle. 45 mins is a common length of UT nap although it does also depend on whether she has yet learned to transition between sleep cycles alone or needs help/teaching.
I would suggest you increase her awake time by 15 mins and then after a couple of days another 15 mins. See how she is on 2hr 30 A time and then perhaps increase by another 15 and see how she goes. She might need an overall increase of an hour (do it is steps though) or she may do well on 2hr 45 for example. Usually at 6 months you are looking for 2 long naps of 1.5 - 2hrs long. If her A time is less than 3hrs and/or naps are shorter you will need to put a CN in to get to the end of the day so that the last A time is not super long before BT.
With the BF it would be more common to see 4 day feeds and 2 night feeds (so there's the 6 in 24hr) but as your LO is sleeping a long stretch at night you are only getting 1 night feed in. I would probably speak with your paedi about extending the times between feeds because generally LOs move to 4hrly E at 4 months (and the signs of needing to move are what you describe, fussiness at the feeds). The idea is not to force her to go hungry but rather to offer a really good feed (like Kate said, the hind milk) and being fussy on the second boob is perhaps indicating that she wasn't hungry enough at 3hrs to take a really good feed. It is not essential to move directly to 4hrly feeds, you can for example move to 3hr 15 or 3hr 30. I think you will find that the E times stretch anyway when the naps extend as she will be asleep and not feel hungry until she wakes.
I wouldn't advise you to go against the medical advise you've been given but I think if you speak with your peadi about her not wanting a full feed at 3hrs they may well advise you to extend a little.
In addition. Usually solids are introduced at 6 months, so you are not far off. Often a top up milk is given directly after solids. LOs should be introduced to a sippy cup (or open cup) of water along with solids as they then need a drink too, they may not take much water but it is practise too. Many people do a top up BF right after (or even during) the solids meal as a "drink". My LO was bottle fed but actually he took more milk per day once he started solids as he needed/wanted a top up bottle right after solids which he would never have taken on its own (mine was on 3hr milk until solids were introduced he couldn't go longer than 3hrs until then) so if there are weight issues with your LO you might find that in a few weeks when you introduce solids (usually one meal per day to begin) she is able to take more milk...additional calories coming from greater interest in milk after solids rather htan the solids themselves if that makes sense. So, even if the naps lengthen and the E times shift to 3hr 30 or 4 hrs or even 5hrs (as solids are established and sleep patterns change it is common for LOs to go longer between their milk feeds) the top up milk feeds at the solids meals will give you those additional BFs that your paedi has advised.
I hope this makes sense. The slight difference being that the main milk times would be 4 per day (eg 7, 11, 3, 7) 1 or 2 at night (eg 10pm and another although your LO skips the second) and the top up feeds come at the solid E times (eg 8, 12, 4).
Hope this helps
