<human>: Can you provide a brief overview of the text?

Hi. I've had my 13-pound bichon-mix for a few months but I'm still a new dog owner. She was a rescue and seems to have quite a bit of anxiety, in general.

However, she was a champ at the dog park. She'd run around all crazy with big dogs, little dogs, chasing, and just seemingly having a ball!! It was so much fun to watch.

The past few weeks, she's stopped playing at the dog park and is "velcro" dog....staying next to me and my spouse. When other dogs approach, she ignores them. ALL of them--big and small.

When a bigger dog approaches her in a friendly way, or sniffs her, her tail goes between her legs and she lunges and barks aggressively so they leave her alone. This behavior came out of nowhere! Why is she suddenly scared?

It makes us sad to see a dog who used to have so much fun at the park regressing and being more fearful. :( The only thing I can imagine is that maybe a big dog really scared her recently at the park (or maybe even hurt her) but we didn't notice it? And now she is scared?
<bot>: My formerly happy-at-the-dog-park little dog is now aggressive towards bigger dogs that smell her and approach her. How can I fix this?