Poco/poca??
When using the word "poco" in front of adjectives does it change to masculine and feminine? E.g. Puedo ser un poca obstinada Or Puedo ser un poco obstinada
2 Answers
Un poco obstinada. In this case un poco serves as an adverb modifying the adjective obstinado- so as an adjective obstinado changes to obstinada, but as an adverb, un poco does not.
As it would be with demasiado obstinada (not demasiada obstinada)
An answer from Lazarus (grammar expert):
https://forum.wordreference.com/threads/un-poco-o-una-poca.638507/
It is a good question indeed! The adverbial construction "un poco + adj" normally modifies adjectives and similar words that agree in number and gender with other words ("Ella" here), but it doesn't change itself. Its function is similar to words like "algo":
Ella es un poco gorda. Él es un poco gordo. Ellos son un poco gordos. Ellas son un poco gordas.
Ella es algo gorda.
Example in use:

Soy un poco obstinado (masc. sing)
Sou un poco obstinada (fem. sing)
Somos un `poco obstinados (masc. pll)
Somos un poco obstinadas. (fem pl)
Invariable