。
She can make her own clothes.
Literal
She [topic-は] her own (Western-style) clothes [object-を] make [possible-ことができる].
洋服 specifically means 'Western-style clothes' — historically a contrast to 和服 (kimono and other traditional Japanese wear). In modern Japanese it's largely interchangeable with 服, since Western dress is the default, but the word retains its morphological transparency: 洋 ('Western') + 服 ('clothes'). ~ことができる is the formal potential construction (literally 'the act of X-ing is possible'), used here in plain past style.