My husband and I had a cookout for a few friends and family, one of our friends brought his live-in girlfriend with him, which neither me or my husband know very well. I made the remark to her that she looked a lot like another friend of ours that was not there, my husband said yes she does but she is a lot prettier. Then this lady said that she loved to hear my husband talk, and that he should be on a 900 sex line. I thought it sounded a lot like they were both hitting on each other. What do you think? Am I just being jealous.

No, I don't think you're jealous. I do think that his comment was to flatter the friend of your neighbors. I do think her comment was not in good taste though she may not have realized it and that may have made you feel uncomfortable being in the middle.
A lot of time we women take in our own measure when another female enters the picture abiet even a party. We also feel the hair on the backs of our necks go up when women notice our husbands. We feel like stamping HE'S MINE across his chest or forehead just to stake our territory.
I'd let it blow over. It was a party. She was a new comer and that was that. No harm done, except to your well being. I say this because you posted here.
Think if the situation was reversed and you were talking to a male friend of your neighbor. Would you flatter him the same way? I've done it. It's just a way to make someone feel at ease.
Now for the 900 phone sex line? Tell her as long as he keeps it unlisted.

I don't think your husband was hitting on her. I also don't think she was hitting on him. But I do the think the comments were both in bad taste but probably not met to be taken that way. If this is the worst problem you and your husband have I think you've got a pretty good marriage.

I think you can pass this off as a stranger who awkwardly was trying to be friendly, and fit in.

I didn't have any problem with his comment, he was just being nice, but when she said he should be on a phone sex line? Wow, especially since they don't know each other