Oh OP, this was me last year.
My dd came to secondary with no close friends from Primary.
I won't lie. The first few weeks/months were really hard work. I found that the girls formed themselves into groups, mainly involving primary friends. Dd wasn't really involved in these. Academically dd loved it from the off. Threw herself into timetables/homework/guitar lessons etc.
I contacted her form tutor after a while to express my little worries. Tutor was very supportive and reassuring, saying dd seemed comfortable and confident. She suggested dd joined the lunchtime Y7 Drama club.
This was a but of a turning point. At Drama club she met lots of children's from different tutor groups. She made friends with different people including many boys. Whilst at drama club it was good. Finding friends in her tutor group was still harder.
By Christmas she'd found a little group of friends in her tutor group, whilst still spending time with Drama club people.
Around March many (girl) friendship groups went into meltdown as old primary friendships seemed to break-up. Luckily dd had no 'baggage' so avoided all this crisis.
By April/May dd had begun to realise that she didn't actually have much in common with the first friends she'd made in her tutor group.
In past few weeks, she's expanded her friendship group hugely, and only now is she truly finding good friends who she really enjoys being with and has lots in common with them.
I don't mean to bore you with detail OP
. I just know how many ups and downs Y7 has brought. If read I Facebook other parents with dcs at different schools (how dare you choose a different school to them! ) like to make out that their child has settled in utterly on the second day and everything is AMAZING. In reality, it's not amazing but it takes time to feel properly comfortable,
In many ways dd had a advantage not knowing anyone from Primary although it was harder at first. Looking back now, I'm so proud of her, she's thrown herself into all aspects of school. I only feel positive for Y8.
To cut a long story short, your dd will be FINE 