Hi Honey! We faced the same issue when my DS was 12 weeks and we went cold turkey to 3.5h EASY - which I think wasn't the best idea!
If you LO is not ready for longer A you can go for a routine like below:
E: 7.00
A: 1hr 30 (7-8:30)
S: 8:30 till 10:00
A: 10:00-10:30
E: 10.30
A: till 11:30
S: 11:30 till 1:00pm
A: 1:00pm till 2pm
E: 2.00pm
A: till 2:30pm
2:30-4:00pm
E: 5:00/5:30pm
S: 5:30-6pm
E: 7.00 (top up)
S: 7.00/7.30pm bed.
In general she shouldn't be sleeping more overall which is tricky with nap transitioning as even with longer A time between naps, sometimes total A during day seems to be less as you eliminated nap! What is working with transitions like that is going from 3xfull naps and 1xcatnap to 2xfull naps and 2xcatnap, and than eliminate 1 catnap slowly so you are finally at 2xnaps and 1xcatnap.