I know my mother qualifies for citizenship under a few rules. She lived there over 5 continuous years under the age of 18, did all her schooling there and she also had all her siblings born in France.
Unfortunately, I don't think that's true. If you are referring to the rules for children born in France to foreign citizens (currently articles 21-7 to 21-11 of the Code civil; similar rules existed between 1973 and 1994 based on articles 44 à 51 of the Code de la nationalité), they only apply to people born in France. Moving to France at the age of two months or being born in a territory that was French a year earlier feels like it's almost the same but it isn't (I happen to know someone who was in this exact situation and was forced to apply for naturalisation and ultimately denied French citizenship, even though his sister, born a couple of years later, was French from birth).
Your mother could have had a path to French citizenship through her siblings (born in France to parents presumably born in French Algeria, they would be French since their birth) but that's not automatic, she would have had to apply for it. I don't think she would be able to do that now that she is not residing in France anymore. Most importantly, if she didn't do it at the time, that means that she wasn't French when you were born (see below).
My question is, can I apply for French citizenship through her? If so, does she need to apply before me? Does it matter that I am now over the age of 18. If someone could help me it would be appreciated.
That's not possible. Naturalisation can have an effect on children but only if they are under 18 and isn't relevant here anyway. All the rules we discussed before would only help you if your mother was already French when you were born (even unknowlingly) but that does not appear to be the case. Consequently, I do not see any special path to French citizenship for you.
Note that the rules that are most relevant are the rules that were in place when your mother grew up, especially the code de la nationalité. Until 1981, the relevant age was 21, not 18.
