I'd address the issue with your friend ahead of time. But I'd also address the issue with your mom and your gentleman friend.
Maybe you can agree with your mother that you will not call her over the weekend. If she knows ahead of time, she won't worry that suddenly you aren't calling her. And your mother could agree to call you only if there's an emergency while you are visiting your friend. Or you will only call your mom twice, or something like that--find a level of contact that you are both comfortable with.
With your gentleman friend, do the same thing. Work out how often you will be in contact, and maybe even when, i.e. you both get up early, so you'll call him every morning at 6:30, and text him a couple of time during the day. Or whatever works for the two of you.
Then, go to your friend. Tell her that you are aware that your phone calls bothered her last time, and explain that you have arranged to limit the number and duration of the calls while you are visiting her.
If she is still upset, you can explain that you are an adult, you have family and other friends that you are accustomed to being in contact with, and that you have greatly limited that contact in order to be with her. But you aren't willing to go days without communication with two very important people in your life, just to be with her. Just as she can get upset about your phone calls, you can get upset, politely, about her need to control your contact with other people.
Four days is a long time to go without talking to anyone other than your host, and I think she needs to realize that. It isn't as though you were spending hours on the phone, ignoring her. You waited until there was an appropriate time, and you made your calls then.
My take on the situation is that she is on some level jealous of your bond with your mother and your friend.