(((BeeGee))) - loving and addict, is certainly full of uncertainty. Yes, there is a chance of relapse(s). But there is just as much a chance of NO relapses. It sounds like this friend is a bit bitter. I'm sure it is hard for her to hear of your daughter doing really well, and knowing her son has relapsed several times.
Put your focus back on today. Today she is clean and working at recovery. None of us knows what tomorrow will bring. I tend to "hope for the best, prepare for the worst". You know she is not "cured", but you also know of addicts who are thriving in recovery.
Don't put too much on what she said. When someone tries to tell me something bad's going to happen in the future, I tell them "well, if it does, I will deal with it then" and then change the conversation. You and your daughter are both working on your recoveries. Today is a good day....enjoy it!
Hugs and prayers!
Amy