My mistake, I assumed you meant she was going to hybrid (Had to help out three of my players hybrid when PH3 was released, lol)
If she's just multiclassing, it should work well enough, but the deeper and deeper she power-swaps the more apparent the gap in stats will be, and the few controller powers she does pick up will be of limited effectiveness. If she's really dedicated to being a part-time controller, then a hybrid would really be the way to go in my opinion. She could keep her striker side with an avenger half as well.
If she's at all interested in an Avenger|Invoker hybrid, it wouldn't be that difficult to change up power descriptions; you could even view Oath of Emnity as twin strike from a fluff standpoint. If she took invoker armor prof she could keep her hide proficency, or take Armor of Faith for very little change. The only challenge being that avengers usually want a big 2h weapon instead of the two she has as a ranger, but investing the feats she would spend multiclassing into some two-weapon feats is a viable alternative. What ever works for her and the campaign ./shrug
If she's just multiclassing, it should work well enough, but the deeper and deeper she power-swaps the more apparent the gap in stats will be, and the few controller powers she does pick up will be of limited effectiveness. If she's really dedicated to being a part-time controller, then a hybrid would really be the way to go in my opinion. She could keep her striker side with an avenger half as well.
If she's at all interested in an Avenger|Invoker hybrid, it wouldn't be that difficult to change up power descriptions; you could even view Oath of Emnity as twin strike from a fluff standpoint. If she took invoker armor prof she could keep her hide proficency, or take Armor of Faith for very little change. The only challenge being that avengers usually want a big 2h weapon instead of the two she has as a ranger, but investing the feats she would spend multiclassing into some two-weapon feats is a viable alternative. What ever works for her and the campaign ./shrug