"to stick to your guns"
to remain steadfast in your opinion or method of doing something even when others criticize or oppose your opinion or method
adamant, bull-headed, dogged, firm, fixed, obdurate, opinion, opinionated, persevere, persevere, relentless, rigid, steadfast, tenacious, tough, unbending, unshakable, willful
This little girl is not going to change her clothes because she is sticking to her guns
when it comes to her choice in fashion ....