I also think that you could allow play dates at your house and under your supervision. It sounds like this girl is a "nice" girl who is easily influenced by a "not so nice" girl. If all parents do not let her socialize with their children she has no choice but to continue to be friends with the trouble maker. I suggest that by allowing her to play with your daughter under your supervision you do have the possibility of positively influencing her.
Whether or not your daughter and she become friends depends on a whole lot of things outside of your control. My granddaughter, who is now in the 5th grade, began choosing her friends before the third grade. Some she talked about at the time and others I'm just hearing about now. My granddaughter was able to choose good influences and remain casual friends with the not so good.
Her mother and I did talk with her about friendship, what it means, and who makes a good friend. She used this knowledge to make her own decisions. She was hurt a couple of times and came to one of us to ask about it. I suggest that by keeping the lines of communication open that your daughter, too, can make good choices.
I also suggest that now is the time to allow her to make choices, when the consequences are small. When she's in middle school she is likely to not consult you and may make a bad choice that involves drugs or some other undesirable content. If she learns about relationships now she'll make better choices later.
I suggest that by having supervised play dates you will be able to talk about what is happening and thus increase her knowledge and skills when it comes to friends.
Either you or your daughter need to return the calls. You want to teach courtesy, too. I suggest that, if you'd let your daughter call anyone else back, that you let her call this girl back. Consistency is important as is compassion. She doesn't have to get involved with the girl. It's just common courtesy to return calls.
I also suggest that if you tell your daughter to lie about missing the phone calls you are teaching her to lie and starting a basis for her to not trust you.
Be courteous, compassionate, and caring as your post indicates you already are. Some of what I say is prompted by other posts.
Yes, you could possibly avoiding difficulties by refusing to let your daughter be involved with this girl. But you also may be preventing some good learning opportunities at an age when the consequences are not so serious.