When my lo was 11 wks old, she started having 45 min naps. At that time, her activity time was 1 hr.
Stacy the nap moderator suggested me to start extending her wake time (nurse n' activity) to 1.5 hr.
increase 10 min every few days.
Lo and behold, after her wake time was 1.5 hr, her nap time extended too. She sleeps 1.5-2 hr.
So, if your lo started having 45 min nap, you could extend her wake time, see if it makes her sleeps longer.