Good or bad for the girls?

[Kira and Cleoh]

So, my mom says that I cant change my girls water 100%, But I want to start with totaly fresh water and clean out their water because their water is mirky, But my mom says that it could kill them because oh shock. But when I first bought them three weeks ago I put them in new water and they showed no unusual activity, Then about a week and a half- two weeks ago I shanged their water about 80% and they were fine. So im thinking changing their water 100% is fine?Now I cant stand if my fish are in mirky water for even an hour because I like to study them and look at them alot. I also cant stand if my fish bowl is too empty, or too cluttered. (Has to be just right.) My mom is very experienced with fish care and breeding, but not with betta's. she has owned some in the past though.
So even if you guys say that it is okay My mom will say "And where did you hear that?" and I will say "on this site," but she wont listen and say not everything you hear on the internet is true. -.- What should I do? listen and change their water bit by bit? Or just change it all together?

[LebronTheBetta]

If you acclimate them, you won't shock them. As long as you're not directly letting them go then you're fine.

[Kira and Cleoh]

Im a little lost.. what do you mean by acclimate them..?

[crowntaillove]

by acclimate she means to let the betta float in his new tank, and to slowly add new water to his current container as to not shock him by tempeture or difference in water parameters.

[LebronTheBetta]

Like, letting them adjust to the water. You would have to float the cup/bag they came with into the tank and let it float there for 30 minutes. Remember they need access to air! And after 30 minutes, you'd have to pour out 50% of the cup/bag water and then little by little, you put in some tank water to let them adjust to the parameters. And when it's full, you gently put the cup/bag into the tank and let the Betta swim out.

[Kira and Cleoh]

Ooh okay! I know what you mean! I'll do that! Thanks guys :)

[LebronTheBetta]

Crowntail made it sound so simple, lol. And no problem.