When I passed my university entrance exam, my mom was happier than anyone else.
When I made it through my entrance exam for university, my mom was even happier than I was.
この場合、次のように言うことができますよ。
ーWhen I passed my university entrance exam, my mom was happier than anyone else.
「大学の入試に合格した時、母が誰よりも喜んでくれた」
was happier than anyone else で「誰よりも喜んでくれた」と言えます。
ーWhen I made it through my entrance exam for university, my mom was even happier than I was.
「大学の入試に合格した時、母は私よりも喜んでくれた」
was even happier than I was で「私よりも喜んでくれた」と言えます。
ご参考まで!