i swapped out my stock 19 incher on my rocker for a 21. at low speeds it's a little harder to keep her stable but it's nothing that she wouldn't be able to handle

 

As long as you don't put drag bars on her ride she'll do just fine. The front wheel will get a little heavier, so no short handlebars, or lowering just the rear end because that will result in a heavier handling, specially on low speeds.

Mimo.

 

Yes, Your bike will track differently for sure. At around 60+ i feel cracks and road lines. I brought my ride to 2 local HD shops and was told that bike tracks like that because of a 700 lbs. bike with a 3" x 21" wheel. And both of my wheels are aligned/neck bearing/spokes/tires/spacers were all checked and everything was correct. The wider the wheel the better off your gonna be. I wouldn't get anything under a 3". I don't see how some of these guys are running 2" wheels on deluxes/heritages. It must ride like $hit on the freeways. Around town i get no wobbles or bad tracking but on the freeways i do feel it. But it's tollerable. Chaz describes it just about right, "BUSIER". The look is baddass....well worth it forsure....

 

It will track in grooves a lot more than the 16", but other than that I don't notice a whole lot. Either way, you get used to it and it just becomes normal after awhile.

If she wants/likes the 16, keep it. It looks and rides just fine with it, but maybe take off the hubcap. The 16 looks a lot better without it, imo.