in this moment it's not possible to get posts by a certain category and show certain posts at the top of the list, but in the next version that I'll release in the next few days, you'll be able to do what you're asking for.
When I'll publish the new version of the plugin, follow these steps:
- create a widget and define the IDs of the posts to retrieve in "Get these posts exactly";
- in "Order posts by" choose "Preserve ID order" (this is a new option I'm adding);
- save the widget;
- create a new widget just below the previous widget
- in this new widget, delete the title and choose the desired category in the "Get posts with this category" field;
- in the "Exclude posts with these ids" field (this is a new option I'm adding), enter the same IDs you used in the previous widget;
- save the widget.
You are done. Test the results. If there is too space between the two widgets, you can reduce it via CSS.
Wait for a couple of days for the new version.