A few years ago on Mother's Day, I gave my mother-in-law a locket as a present.

Literal

Several-years-ago [attributive-の] Mother's-Day [on-に], mother-in-law [dative-に] locket [object-を] present-did-[polite-ました].

A straightforward polite narrative sentence. 義母 ('mother-in-law') uses the prefix 義 for relatives acquired through marriage — similarly 義父 (father-in-law), 義兄 (brother-in-law). It contrasts with 実母 ('biological mother'). ロケット is 'locket' the jewelry pendant — identical spelling to 'rocket,' disambiguated by context. プレゼントする is the loanword+する verb for 'to give as a present.'