Does Lilia mix languages in a single phrase? She sure does.
There are patterns, though, she does not do it randomly.
She will mix Arabic and French. That's absolutely normal, given that half of the Maghreb does it as well. She does know that there is a difference, though.
We once had French friends over for a visit. It took Lilia a day or so before she realised that our friends and their children did speak French but not Arabic.
And, when she visits her grandparents in Algeria, she will drop French quickly and speak Arabic exclusively.
She will sometimes mix English and German when she talks to me, eg. "I want Buch lesen". I think she feels that English and German are somewhat close.
And if she does not know a specific word in the language she is currently speaking, she sometimes thinks for a second, then tries words in other languages to see if we understand them. Or, if we are both around, she will turn to the other person and say the word in their language, so the other person can translate.