In the ordinary way of things, you wouldn't be referring to "her" or "his" without some context, so it would likely be apparent. In the situation where you do need to make it clear, French uses something called the emphatic pronouns.
"Elle a conduit sa voiture à lui, et sa voiture à elle" = She drove his car and her car.
I think I have that right. Francophones, please confirm or correct.
The past participle does not agree with the subject of the sentence but with the direct object of the verb, and that is only when the direct object appears before the verb. See my note above: J'avais étudié la leçon que le professeur a expliquée. The past participle in J'avais étudié uses the masculine form because there is no direct object before the verb. However, by the time you get to the end of the sentence, there is the reference to "la leçon" which is the direct object of the verb expliquer, so it must agree, ...que le professeur a expliquée.
I'm glad to hear that! Be aware that the English "past perfect" is actually not Passé composé. Because Passé composé is a past tense, we are tempted to say "past perfect" but it is actually "present perfect" (which is a past tense). Confusing, isn't it? English "past perfect" is the same as the French plus-que-parfait (which refers to a previous past action). Unfortunately, Passé composé does not map to a specific English tense though it is most commonly translated as English Simple Past (I drove) or Present Perfect (I have driven). There are even a few other possibilities which are sometimes appropriate but are not applicable in all cases (e.g., English present perfect continuous). Even the Present Perfect version in English sometimes sounds "off".
Well there is not supposed to be a break between elle and a so it would sound like [ELLA].
Besides, your proposed sentence sounds like "she drove it her car" which does not make sense. If the noun "her car" (sa voiture) was not there, then elle l'a conduit ("she drove it") would have worked, where the pronoun la replaces "her car".
Aldo is right. The difference between "has driven" and "had driven" is confusing to some. The "has driven" comes from Passé composé "elle a conduit" (also "drove"), and the "had driven" comes from the Pluperfect tense "elle avait conduit". The Pluperfect tense is used to refer to an action in the past which occurred before another action in the past (usually expressed in Passé composé or Imperfect). Two examples:
- J'avais étudié la leçon que le professeur a expliquée = I had studied the lesson which the teacher explained. First I studied the lesson; then the teacher explained it. Both actions are in the past. The action that occurred in the past before the other past action is in the Pluperfect.
- J'ai étudié la leçon que le professeur avait expliquée = I studied the lesson which the teacher had explained. In other words, the teacher explained the lesson first and then I studied it.