Whats it mean when profile doesnt appear in search.

My brothers partner has been off line to him. She doesn't show in search, but can get to her profile thrue the information where partners are on his profile, she is not listed in any of the groups she actually has listed in her profile. So we cant tell her last day online. I even added a group just to see if she was in that one, and nothing.

Does this mean she deleted her account? And now is hiding?

She could have cancelled her account, or she could have fallen behind on payments if she was premium/a sim owner, or she could have been banned.

There's really no way to know, and LL as a rule wouldn't tell you what happened although in some cases they might point out which of the three caused her account to get suspended but don't count on it though.

Don't know about the groups thing, but she could have unchecked the "Show in search" option in her profile. This would prevent her profile from showing in search.

She may have muted you, you brother, or everyone in her friends list. From what I understand, mute doesn't only stop chat. Ask someone else, who isn't in her friends list, to do the same checking as you've already done. It may get some results.