At 5 months, you can probably look at adding more A - the av is around 2.5hrs, some do more and some less. It might be that she's not tired enough to sleep longer because his A is short. We worked on 1 A at a time and we added 10-15min increments every couple of days so if she's only used to being awake for 1.5hrs, you wouldn't jump to 2.5 right away... try working on it slowly. Also, when she wakes, I would leave her in the cot to see if she will put himself back to sleep. I found that was the best way for my DD to learn - of course, if she's crying and its not a mantra cry, you would go back to him and try and resettle her. Does she go to sleep independently?
With regards to feeds, I would try and stretch her to at least 3.5hrs. My LO is also breastfed and was on 3.5hrs for a long time. When we went to 2 naps around 5-5.5months, she started sleeping better during the day and subsequently her feeds extended to 4hrs.