I'm Lucy, and I'd be happy to answer your questions today.
Typically, any person who owns a property can give consent for another person to enter. However, in practice, that tends to work better when the person granting access to the property is also there. If you or your daughter show up on your own over the girlfriend's objection, there's no way to stop her from calling the police. It would be to your benefit to print a letter from your ex-husband giving her consent to enter and asking police to go with you to get the items.
Also note that, if your daughter doesn't have a key, she will have to work with the girlfriend to ensure that she's there before going over to the house. Police can help stop her from denying you entry, but if she's not there and the doors are locked, they can't let you in.
Your ex-husband can sue his girlfriend for conversion if she prevents him from claiming his belongings. He could try sending her a message now stating that she will be sued if she continues to interfere with you and your daughter. That's the other option.
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