No. You only agree when you use «essere» or when «lo»/«la«/«l'»/«li»/«le»/«mi»/«ci»/«vi»/«ne» come before «avere»
aperto is the past participle for aprire. Verbs conjugated with "avere" do not change past participle endings based on number and gender in the passato prossimo.
With direct object pronouns, you are correct. For example "Lei ha aperto la finestra?" "Si, l'ha aperta"
the fast translation is DEFINITELY wrong, it says Mi instead of ha. I can't report it because my report button does not work. I am using Safari 5.1.1
So is this simple past tense or past participle? Because it accepts ''she opened the window'' and ''she has opened the window''....
"past participle" is the word "opened" when it comes after "has;" in Italian, it would be «aperto». I think you mean whether this is the simple past tense or present perfect. The fact is that it can translate as both; you would use the compound passato prossimo tense for both the English simple past and present perfect.