We towed a Pup with a Sienna for years. Loaded for travel, it was right at 3500. The Sienna was a great tow vehicle for it. It did come stock with a trans cooler so I didn't have to deal with that. Your daughter will need to confirm if her van has a trans cooler or not. I did add airbags to the rear springs. Unfortunately, this is the downside of using a minivan for towing. They are designed to carry people in comfort so the rear suspension is soft. Unless the Pup is pretty light, you will want to have your daughter upgrade the rear suspension with bags (if available) or some other spring support. No, it does not increase the towing/carrying capacity, just helps the van not sag as much. The bags also helped a lot when we had the bike rack on the van with the bikes so the hitch didn't drag on every driveway.
As has been mentioned, she will need a brake controller and likely a seven pin plug installed. I also echo the sway control as well. While I never had any sway issues, I did use a friction sway control. Not the best option, but pretty much all that was available for towing with the van.
I don't remember if you mentioned it, but obviously she will need a 2" receiver installed. One thing she may want to consider unless she plans to continue to tow in the future, she may can rent something that will tow it for about the same cost as she is going to spend getting the van set up, especially if she has to pay someone to add a trans cooler.
It can be done with the van safely as long as the Pup is not too big.
