I too have a 7.5 monthold and am battling with the same dillema, except that on most days, my dd only naps for 45 mins, so it is almost impossible to drop the third nap. If i were u i'd keep upping that A time and maybe, if u can, for that catnap try getting outside with the stroller for a walk, let her sleep for 15-20 mins instead of 35. OR move the bedtime to 6, and slowly stretcxh it by 10 mins every day till u get back to a 7pm bedtime.
Just a few suggestions. Also for me, i know that getting outside helps keep dd up longer and happier, keep changing scenery, or jus carry her around. When dd Does have 2 good naps, she can usually go 3.5-4 hrs in the late aft. But unfortunately for us, good naps are a rare occurance. HTH
Sheri