"Her ovens are big."

Translation: Cuptoarele sale sunt mari.

[SamuelRias1]

Isn't cuptor a masculine noun, if so, why does it end in ele?

[natomist]

Cuptor is neutru masculine. Un cuptor - două cuptoare. So we should use femeie form with plural.

[Jill635577]

The adjective mari/mare keeps giving me trouble. What are the rules with this adjective?

[crbratu]

Nothing special here. The adjectives have in general 4 forms as they have to be in accordance with the noun (masc sg / fem sg / masc pl / fem pl) Example: bun / bună / buni / bune.
Some adjectives are though less complicated because they have the same form for masc. and fem. , therefore only 2 possible forms remain (sg / pl).
This is the case of mare (masc. or fem sg.)/ mari (masc. or fem pl.)
Similar to other adjectives ending in ”e” (tare / tari; rece / reci; limpede / limpezi; iute / iuți; fierbinte / fierbinți; etc.)

[Anniechisk]

I thought "ei" and "a sa" was hers. So does sale mean hers too?

[crbratu]

It's the feminine plural form. Iepurele său/ iepurii săi/ găina sa / găinile sale