i would definitely tell her how you *really* feel. imagine for a second she get's her hair trimmed to a bob [or even shorter] and tells you afterwards that she thought you didn't mind, 'cause you never said anything!
Just tell her, most women love a compliment.
Now imagine for a second you do tell her, and she's actually going to enjoy all the things you would want to do to her hair...
now that sounds a lot more like an acceptable thought, don't you think?
keep us updated, i'm really curious where this goes.