Can I take recommendation from someone I met at a conference? I met a faculty (from a university in the UK) at a conference. She liked and praised my work and we are in touch after conference. She has an impressive profile and her research work is similar to mine. Is it okay to take a recommendation letter from her to seek postdoctoral position overseas? Will it help?
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?