Make sure you check the lists countries that are restricted on the gambling site terms of service, if the country you are living is not there, you can download the gambling site mobile app which will be to bypass the ISP blocking. But many gambling sites do not have mobile apps which can make it difficult.
Even if the gambling site has the mobile apps I wouldn't going to download that because most of the time I played on the desktop or in my laptop. And also, downloading apps is just like extra hassle for me.
The second is that you can contact her gambling site customer care to ask the question. But before that, you can try to access the gambling site through a mirror link to see if it will work. Make use of the legit mirror link and not fake one.
Thanks for the idea, I think it would be the best option, I remember that even before this, I used to face the same problem with direct links to bc.game or any other website, which I would later access through a mirror link.
Another option for you is Tor.
However gambling platform often block Tor exit nodes, and performance can be worse than that of a VPN.

In fact, if direct Tor connections are blocked due to censorship then you can try using bridges, obfs4, Snowflake or WebTunnel.
Haha, TOR would be the worst option. I am saying from the experience of mine, I already tried that site on tor browser it's really worse than VPN, And while using it is pretty much the same as using a VPN, I was simply looking for a way to access without VPN or TOR.
I would be a bit cautious about using random free proxy service. I am not sure how wise it is to trust any unknown proxy operator. Especially when entering login credential, password or payment and withdrawal details for gambling account.
Even with HTTPS, proxy operator would still have access to connection metadata and information regarding your traffic routing.
Thanks for the caution, I actually forgot about these things, reason is I used the proxy server a long time ago.
So, my approach would be to first determine whether that blocking is occurring at DNS level or network level, and then use trusted solution. And if mobile data works fine then simply switching ISP would be easiest workaround.
You don't necessarily have to buy VPN to solve every problem.
Actually, mobile data is not always available or I don't get the same speed, which is why I'm basically trying to find other options, however, I'm now trying to find out if there is a mirror site for the platform I'll be playing on.