My fiance's sister is very protective towards her brother, will she eventually warm up?

We're currently long-distance (have already met once in person on Nov 2023, spent quality time for a week but clicked very well.. and very fast) but planning on solving this by getting married within 5 weeks.

My fiance's mother passed away 2-3 years ago due to medical negligence but he has several brothers, a father and only one sister. He showed her our wedding invitation and she immediately bombarded me with messages, asking what's my agenda, why I'm still single at nearly 40 (I'm 37), where I work at and more questions. I understand but it felt like an interrogation. She has expressed her concerns and clearly is distrustful.

This is the first time I've ever been questioned like that. I was shocked to be honest. She expressed how her brother is very loved her all his family and isn't convinced how we can get married in a shorter time. Wow, I've never been in the position of having to prove someone wrong, of being questioned myself. He's 50 but his sister is very protective. The way she messaged sounded like protective momma bear mode, wow. Will she eventually warm up?

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I have no personal agenda. I just want her brother, to be permanently with him, to his loyal lifetime partner.
My fiance's sister is very protective towards her brother, will she eventually warm up?
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