I'd say that if she's willing to buy it for you, you should get the t3i. Also, if you're wanting to learn about photography, you shouldn't get a webcam. Third, if you you do get the t3i, you don't have to get another piece of software - it comes with Canon EOS Utilities (no onion-skinning). And finally, if you choose on getting a webcam, I'd recommend the c910 with a mac, and the c920 with a PC (I don't have a mac though, so you'd want to research the c910).
Hope this helps a bit.

-LG501

2nd place Darkness and Light entry: The Tree
Behind the Scenes

Before you choose the Canon EOS 600D/T3i, please take the following into consideration:
- To date, you are unable to have live-view on iStopmotion with a DSLR. This means you shall effectively have to upload every frame from the camera to iStopmotion (through a thing called 'PTP Mode'), which means the absence of useful features like onion-skinning. I asked Boinx on their forums a few months ago if they would ever add this much requested feature, and they basically said they would in the somewhat near future.
- As with the above point, you'll have use another type of capture software (for now!) to get live view, such as DragonFrame ($300) or the included EOS Utility, which I don't know much about... sorry.
- If you want to get into photography, the T3i is a fantastic camera. You're tossing up between an 18MP camera or a 3MP webcam.

Webcams are:
- Cheaper... probably doesn't matter in this instance
- They are more manoeuvrable is smaller sets.
- They have a much lower, yet still very good, resolution when compared to DSLRs.

There's some food for thought... hopefully it hasn't created more reservations about your choice!