I dunno? Are there any benefits to selling the car in the same state that it is currently registered in (assuming it was registered in your state)? Also, I assume that when she signs the papers she will have her signature notorized as well? Your notary couldn't notorize her signature if it was on there before hand (and if only in her late husband's name, you would need the papers that show that she is authorized to sign it).
Also, from my understanding TrialPay is not a 3rd party go-between for transactions like this. I thought it was a place where you could offer a service or digital media, but customers pay for them by doing free trials on products, etc, instead of giving money... This makes me think it is very fishy, but TrialPay doesn't ask YOU for money, so it would be a very stupid scam.... lol