Ex-girlfriend Gave Me Cash Toward A Truck, Said It Was A Gift, Now Threatening To Sue Me After Breakup (wa/or)

Hey everyone, looking for some advice on a situation with an ex. This started in Washington, but I’ve since moved to Oregon. About three months ago, I found a truck on Marketplace for $4,500. I only had $2,500 on me and told my girlfriend at the time I couldn't afford it. She insisted on giving me the remaining $2,000 because she wanted to see me happy. I actually turned her down at first, but she kept pushing until I accepted. There was never any talk of it being a loan, no repayment plan, no "pay me back when you can," and zero talk of shared ownership. Everything was verbal over the phone; there are no texts or emails about this money. When we met the seller, she handed me an envelope with $2,000 cash. I added my $2,500 and handed the full amount to the seller myself. The bill of sale and the title were signed over to me only. Her name isn't on anything. I still have the signed WA title and bill of sale, but I haven’t gotten around to transferring it to Oregon yet. We broke up a couple months ago and I went no-contact. Now she’s messaging my sister saying she’s suing me to get the $2k back. She never once asked for the money before this. I have a few questions: 1. Does she actually have a leg to stand on legally to get that money back? 2. Does the fact that it was cash with no written contract make it harder for her? 3. Does having the title/bill of sale in only my name prove I'm the sole owner? 4. Should I rush to transfer the title to Oregon now to protect myself? 5. If this goes to small claims, what kind of evidence actually matters here? I'm just trying to figure out if I need to worry or if this is just an empty threat. Thanks. Location: OR/WA