She may be lower sleep needs - or rather she may be one who prefers to consolidate her sleep at night, rather than in the day, though overall sleep totals aren't especially 'low'. Because she is so young right now I would continue to be a bit flexible, it may be that she can handle the odd 1-nap day for now with some big A times, but not every day. It's young to be on 1 nap totally, but we do see some babies who start to transition around now. Bear in mind the transition can take several weeks to months, especially for those starting early so continue to follow her cues and give two naps where she needs. I think her A times are pretty average for 8 months right now - and if she has to fit around brother's routine it may be you don't have that much in the way of flexibility to experiment with pushing them. Do you have set times you need to be out and about?