The old woman breathed a sigh of relief and smiled warmly.

Literal

Old-woman [topic-は] relievedly breath drew [and-て] warmly smiled.

Two 擬態語 in one sentence: ほっと captures the release of tension (a sigh of relief), and にっこり describes a warm, gentle smile. Japanese's rich mimetic vocabulary lets a short sentence convey nuanced emotional texture that English needs more words for.