3 years old lighting Shabbos candles
My almost 3-year-old does not fully speak yet. She can repeat words. But when I am making the Brocha on the Shabbos candles at some point, she stops repeating each word. She is turning 3 tomorrow evening, should she light this upcoming Shabbos with making a Brocha on Shabbos candles and saying a Brocha Shehecheyanu? Or should she wait until Shavous to light and make Shehecheyanu?
From your question I assume you are aware of our Minhag that a girl begins lighting Shabbos (and Yom Tov) candles even before she turns 3, as soon as she’s able to say the Brocho(s) – as mentioned here on point #3
Regarding saying Shehecheyanu the first time she lights, see there as well, point #4. Consequently, she can start lighting even this week, by wearing a new garment. (There is no issue of saying Shehecheyanu during Sefira in this case).
Important note: One may only light Shabbos candles after the Zman of Plag Hamincha (point #1 in the abovementioned link). Regarding lighting early on Erev Shavuos, see here.