In "To Kill a Mockingbird" did Mayella actually kiss Tom, or did she just tempt him like Atticus proposed?
There is only one person who has been willing to tell the truth about this matter, and that is Tom Robinson himself. So, we have to look to his testimony to find out exactly what happened. In chapter 19, we get Tom's side of things. He describes how Mayella had him come in, then asked him to get something off of the chiffarobe; he grabbed a chair, did so, and then Mayella grabbed him around the legs, then hugged him around the waist, and then, "she reached up an' kissed me 'side of th' face." So, according to Tom Robinson, she did kiss him, on the side of the face. She then attempted to tempt him into kissing her back, saying, "Kiss me back, nigger". Tom wasn't having any of that and got out of there as fast as he could. So yes, Mayella did actually kiss Tom (if you believe him over her, that is), AND attempted to get him to kiss her back, just as Atticus hinted.
This answer hinges upon whose testimony you choose to believe. Tom says that Mayella grabbed him around the legs, then the waist, then kissed the side of his face. He also says that she claimed she had never kissed a grown man before and that she decided she might as well kiss him.
Mayella's story, however, is totally different. She claims she was accosted by Tom, and that he threw her about, choked her, beat her, and took advantage of her sexually. This story is refuted by Tom's testimony and other details provided in court. Here again, this answer depends on which testimony you choose to believe.
We never see the event from an objective perspective, so the answer to this depends on who you believe. If you believe Mayella, then no, she neither kissed Tom nor tempted him. If you believe Tom, then she did more than tempt him: she kissed him. Remember that he says, " “She says she never kissed a grown man before an’ she might as well kiss a nigger. She says what her papa do to her don’t count.”
Personally, I believe Tom. She kissed him, and would have done more than that, frustrated and trapped as she was.