Can I take recommendation from someone I met at a conference?

There's nothing stopping you asking for one. However, you need to consider what would be written in such a letter.

In short, you can ask for a letter, but be careful how you use it. What could the person say on your behalf if a potential employer contacts them to get more information about their assessment of you?

For instance, it doesn't seem that you have a professional relationship - you haven't co-authored papers, nor have you worked together in the same institution, nor have you served on the same committees, etc. Any of these things is not necessary, of course, but these are the sort of things a referee would cite as evidence that they are in a position to recommend you or your work.

However, it sounds like your contact does know of your work. However, are they a world-leader in your field? Do they have the respect of your community? When they say good things about you or anyone else, do others pay attention?

How will a reader interpret a reference letter that is based only on a familiarity of your published work, and a single meeting at a conference?

It’s best for people applying for postdocs to have at least one letter from a well-known researcher in the field who is not at their school. It is quite typical that this person has only seen you talk once or twice and has read your work. Of course your advisor’s letter will have more detail and first-hand experience, but an outside perspective on the value of your research is a valuable addition. You should definitely ask for a letter from this professor!

You can definitely ask her for a letter of recommendation. It cannot hurt I assume.

However, considering that the person does not know you much, the letter might not have much weight in the eyes of whoever reads it.

Since there is not much to lose, ask for the letter. If you receive it, use it as you see fit. There is no guarantee whether it will help or will be useless.