I wouldn't make the full jump from her current 2.5h A time to 3h all at once. Try letting her do 2h40 and see what her naps look like. If she gets a good 1.5h nap for both naps, then leave the A time there. If she's still giving you 45 minute naps, then increase again. If you suddenly get 30 minute naps, scale back by ~5 minutes.
Still offer her a catnap in the pm, just to see her through until bedtime. She'll probably be UT as it won't fall in her sleep window anymore, but from what other moms have said, they will APOP to get the zzzs in
If she refuses to go down, move her bedtime forward. If after about a week she is still refusing to catnap, then start increasing her A time more. You can also keep gradually increasing A time by 5 minutes here and there, allowing that she doesn't become OT.
Also, I would consider dropping the DF, especially since it sounds like she's not taking that much anymore. You can drop it cold turkey, if you think it will be okay. Or there's a gradual way, too (link below).
HTH!
http://babywhispererforums.com/index.php?topic=54662.0