Hi there. 1.5 hours A time (including winddown) is average for 3 months old, but your dd could need a bit less, especially with the short naps. Also, as motion sleep is not the most restorative sleep, she is probably less rested when she wakes.
It's challenging with an older sibling--does the sibling still nap? Some moms have altered the "standard" routine to sync their two lo's naps, so the a.m. nap is puposefully shorter and on the go, and then both the toddler and the baby nap in the afternoon at home. It would be good if she could get at least one crib nap per day. Many moms also do the catnap on the go, as this nap is supposed to be short and will be dropped at some point.
Just FYI, if you plan on staying with the on-the-go naps you might want to plan for shorter 40 minute naps and adjust your routine for shorter A times (you may need an additional nap during the day too). 40 mins isn't really considered "short" for a stroller nap--many lo's don't nap beyond this on this go.
HTH,
Malia