You're in a better place than most writers for a number of reasons:
- An agent loves your work--and enough to call. This means even more than an "I love this" via email--and it means other agents are likely to feel similarly. It probably means that your writing is great, but you made some choices in the storytelling that could (in her mind) be stronger. This is far easier to work with than someone with a fabulous premise who does not write well.
- You got good vibes. It's hard to fake vibes over the phone.
- She already started making changes--which makes it more likely she'll ask for more changes, rather than just say no, if she doesn't like this version. It's like people who walk into a house they're considering buying and say, "Oh, honey! Our sectional couch would look great in that corner!" "Yes, sweetie, and wouldn't this room look great in a pale marmalade?" "Why yes! It would go with my porcelain pigs collection! We could put a shelf there..."
- If she does say no, she'll likely be helpful about it.
- If this work doesn't get picked up, she's very likely to want to see the next.