Ancestry DNA advice 😐

Let me start by saying, my sister has given me permission to post about her story/experience, in hopes of getting advice.

This is probably going to be pretty long, but I hope you will take the time to read it all.

We know genetics can be weird.

Okay, so after our maternal grandparents did ancestry DNA my sister was intrigued and wanted to know her genetic makeup. Our mother is basically completely white (European) with some Native American (according to her parents ancestry dna) and our father is half white and half Filipino (his parents havent done the DNA tests to our knowledge but our grandparents met when my gpa was deployed in the Philippines and they got married and she came back here with him).

Our whole lives, my sister has been told she looks just like mom with light brown hair and light eyes and I look like dad with dark hair and dark eyes. She looks nothing like Dad except having dark skin and I look a little like mom and have very fair skin like her as well.

My sister got her results back and to our shock she had not even .1% of Asian anything. She was mostly German and Italian. Italian did not show up for my maternal grandparents, meaning that had to come from her paternal side.

She panicked and called our mom and asked her what she thought. Our mom got really upset. Not mad. But scared. She said before she got pregnant with my sister our dad cheated and they broke up but they still hooked up and that she was going through some stuff and partied a lot and she said she honestly doesnt remember if she had sex with someone else around the time my sister was conceived. But when she found out she was pregnant she told my dad, they got back together and got married and they are still together 30 years later.

Moving on..for anyone who doesn't know, when you do the test it will match with people you are related by DNA and tell you what kind of relative you are or around what you could me (like 2nd 3rd 4th cousin). She dna matched to our maternal grandparents, and some cousins and distant family that we know on our moms side. Then she connected to few people that it said they were first cousins that we had never heard of and werent connected to anyone on our moms side, meaning they had to come from our Dads side. Thing is, we know all of our cousins on our dads side. He has two sisters and one had two children, neither if which were the people that matched DNA.

NOBODY with our Dads last name or any name from our fathers side matched to her. It was dozens of people that were pretty closely related to her that we had never heard of and did not match to our grandparents on our mothers side.

Some of my theories are:

1. Simply..Dad is not her dad.

2. Our Paternal Gpa had other children that he never knew about and dont have his last name or he kept them a secret and they had their moms last name

3. Maybe our great grandparents had more children that we dont know about?

I just dont know. She is having a major identity crisis and our mom is terrified of what could come from this and is insisting my sister just drop it. Our Dad gave us the world and continues to help us into adulthood and my mom thinks she should just be happy with the dad she has and not look into it. But..if I were in my sisters shoes I would want to know for sure..it doesnt void everything our dad has done for her but it would be nice to know..we havent told our Dad anything so he doesnt get upset..

She asked if I would do Ancestry DNA because it will show if we are full or half siblings. But what if I match to my dads family and they see they dont match to my sister and they say something to my Dad..

What's your advice...?